FAQ: Classical swine fever

Classical swine fever (CSF) is a highly contagious viral disease of pigs. Virulent strains of CSFV cause high mortality in pigs. The disease is maintained in pigs by subclinical mothers giving birth to infected piglets.

CSF is caused by the Classical swine fever virus (CSFV), which belongs to the genus Pestivirus within the family Flaviviridae, and is closely related to other ruminant Pestiviruses such as Bovine Viral Diarrhoea virus (BVDV). The incubation period of the disease is 2-14 days, with death occurring 5-15 days post onset of clinical signs.

CSF is caused by the Classical swine fever virus (CSFV), which belongs to the genus Pestivirus within the family Flaviviridae, and is closely related to other ruminant Pestiviruses such as Bovine Viral Diarrhoea virus (BVDV). The incubation period of the disease is 2-14 days, with death occurring 5-15 days post onset of clinical signs.

As of early 2009, the latest incident of disease was in a wild boar piglet in the North Rhine Westphalia region of Germany that was diagnosed as having CSF. In May 2008, an outbreak occurred in Backyard pigs in the Kjustendill province of western Bulgaria.

The clinical signs of CSF can occur in either chronic or acute form. In pigs, the acute form is preceded by a raised temperature (40.5ºC), and a loss of appetite (anorexia) and lethargy. A number of other clinical signs can occur, including: Constipation followed by diarrhoea, haemorrhagic lesions of the skin, cyanosis of the skin (especially in the extremities), ataxia, spontaneous abortion and coughing. Pigs that display chronic clinical signs of CSF infection, may also be pyrexic, have extended diarrhoea, or show apparent recovery from disease, before relapsing and dying. Mortality rates from CSFV infection in young pigs is extremely high.

CSFV will be disseminated throughout a pig that has died of the infection, for this reason, the main source of spread appears to be from pigs being fed infected pork products. CSFV can survive in the environment for a long time, so that transmission by contaminated clothes, vehicles, and equipment is also possible. Pigs can also be healthy whilst incubating the infection, or have recovered from infection but continue to excrete virus for long periods of time.

The differential diagnosis for CSF is extensive, including African Swine Fever (ASF), Salmonellosis, Infection with bovine viral diarrhoea virus, leptospirosis, Erysipelas or Coumarin poisoning. Diagnosis of CSFV is done either by identification of the virus with a direct immunofluorescence test on cryostat sections of organs, or viral isolation on cell culture, or with serological techniques such as Neutralisation peroxidase-linked assay, fluorescent antibody virus neutralisation, or ELISA.

As there is no effective treatment to CSF, any pig affected by disease must be slaughtered. Due the routes of spread of the virus (see above), effective disposal of the carcases (by burying or incineration) is essential to limit the spread of the infection. Preventative controls relying on policies for protecting herds from the virus, including strict import and quarantine policies for live pigs, effective surveillance and disease reporting strategies, this will include farmers being aware of the disease, and taking an active role on checking their herds for CSFV infection. Although prohibited in CSF free countries, vaccination with a modified live virus is effective a preventing disease in countries where the disease is endemic.

Following the positive diagnosis of CSF on a premises, usually the pig herd will be slaughtered as a preventative measure. The carcases, bedding and feed etc. will be disposed of and the affected premises thoroughly disinfected. Control zones are set up, and pig movements within this area are controlled. Surveillance within and around the control zone with study of the epidemiology of the outbreak are looked at (possibly tracing entry points of the infection and possible routes of spread).

Classical swine fever (CSF) is caused by a small RNA virus with a lipid envelope, the Classical swine fever virus. The virus, which was previously called Hog cholera virus, is closely related to the ruminant pestiviruses which cause Bovine viral diarrhoea and Border disease of sheep. Current CSF viral strains which circulate in different parts of the world are of varying virulence, i.e. they may cause mild, medium, or severe symptoms.

The outcome of classical swine fever strongly depends on the age and, to a lesser extent on the bread, of the infected pigs and the virulence of the infecting strain. A wide range of symptoms are possible. The most severe symptoms can be observed in piglets and young pigs. In older breeding pigs the course of the infection is often mild or even almost asymptomatic.
After introduction of the virus in a susceptible herd the first symptoms are fever, lack of appetite and lethargy. The pigs often huddle together. These symptoms can easily be mistaken for other diseases. Further symptoms of the acute disease are haemorrhagic lesion of the skin, multifocal hyperaemia, conjunctivitis, cyanosis of the extremities, diarrhoea, dyspnoea and coughing. Occasionally the animals vomit, show ataxia, paresis or convulsions. The mortality in young pigs may be as high as 90%. Acutely diseased animals usually die 5 to 15 days after onset of the illness. The chronic form of the disease is more seldom.
The initial signs are similar to the acute infection. Later the pigs develop non-specific symptoms, e.g. intermittent fever, diarrhoea and wasting. Animals can survive 2-3 month before they relapse and die.
Congenital form: CSFV can be transmitted during pregnancy from the sow to the fetuses. Infection during early pregnancy results in abortions, stillbirths, mummification or malformations. Infection of sows at up to 90 days of pregnancy can lead to the birth of persistently infected piglets, which may be clinically normal at birth and survive for several months. After birth they may show poor growth, wasting or occasionally congenital tremor. This course of infection is referred to as "late onset CSF". These piglets may play a crucial role in spreading the disease and in the maintenance of virus persistence within a population as they constantly shed virus until death. Infection during late pregnancy may result in the birth of weak piglets, which grow poorly and die later.

Pigs and wild boar are the only natural reservoir of classical swine fever virus.

The main natural route of infection is horizontal,e.g. oronasally by direct or indirect contact with infected pigs. The virus is excreted by diseased animals and already during incubation with all secretions and excretions. Congenitally infected persistently viraemic piglets spread high amounts of virus until they die. Within a herd the virus is mainly transmitted by direct contact. The transmission to other holdings may occur via visitors, veterinarians or pig traders by contaminated clothes, vehicles, instruments etc. In areas with a high density of pigs spread of virus easily occurs between neighbouring pig holdings. Disease transmission via semen of infected boars may also occur. Within the EU the feeding of swill to pigs is prohibited. However, especially in private backyard holdings this ban is difficult to enforce and feeding of virus contaminated food can be the cause of CSF outbreaks. Another route of infection is direct or indirect contact between backyard pigs and wild boar.

In the European Union prophylactic vaccination of pigs against CSF is prohibited. However, emergency vaccination can be part of the control strategy in case of a contingency. Either conventional vaccines or a marker vaccine can be used for the control of CSF in the event of an outbreak. Conventional vaccines, which were used until 1989 for large scale prophylactic vaccination, base upon attenuated virus strains. With the help of marker vaccines a differentiation is possible between infected and vaccinated animals (DIVA). The marker vaccines which are commercially available base on genetically engineered virus proteins (subunit vaccines). New recombinant marker vaccines, based on chimeric viruses are under development.

CSF is still endemic in the wild boar populations of several European countries and in domestic pigs of several Asian, and Central and South American countries. There is a constant threat of introduction of the disease to susceptible pig populations by direct contact of the pigs to wild boar or by indirect contacts (import of infected meat or meat products, infected equipment, vehicles etc.)

In countries which have eradicated CSF (as it is the situation in most of the EU member states) a non-vaccination policy (combined with stamping-out in cases of an outbreak) is applied. In order to prevent the introduction from countries with an uncontrolled CSF situation import bans for animals or their products are in place. Within the EU feeding of swill to pigs is prohibited. In case of febrile disease with unclear etiology in some European countries farmers or veterinarians can submit samples for CSF exclusion diagnostics to the laboratories free of charge to improve early detection in case of an outbreak.

An important differential diagnosis is African Swine Fever (ASF), a fulminantly progressing hemorrhagic disease. Except for Sardinia, the EU and its neighbours are free of ASF As clinical signs of CSF are often rather non-specific and depend on factors as: age group and individual health status of the animals and virulence of the CSFV strain many other diseases must be considered for differential diagnosis. All clinical pictures accompanied by high fever and general symptoms in the respiratory, gastrointestinal, reproductive tract and/or central nervous system should be regarded as possibly induced by CSFV. List of possible differential diagnosis (in brackets: shared symptom complexes with CSF) o Actinobacillus pleuropneumoniae (skin alterations, respiratory symptoms) o Actinobacillus suis septicaemia (skin alterations) o Aujeszky`s disease (reproduction problems, CNS and respiratory symptoms) o Brachyspira hyodysenteriae (gastrointestinal problems) o Brucella suis (reproduction problems) o Eperythrozoon suis (skin alterations) o E.coli septicaemia (skin alterations, gastrointestinal symptoms) o Erysipelothrix rhusiopathiae (skin alterations) o Haemophilus parasuis (skin alterations, CNS symptoms) o Intoxication (CNS symptoms) o Lawsonia intracellularis – PIA (wasting, gastrointestinal problems) o Leptospira (reproduction problems) o Meningococcus (CNS symptoms) o Pasteurella multocida septicaemia (skin alterations) o Porcine circovirus 2 (skin alterations, respiratory symptoms, wasting) o Porcine Parvo virus (reproduction problems) o Porcine Teschovirus 1 (CNS symptoms) o PRRSV (skin alterations, respiratory symptoms, reproduction problems, wasting) o Salmonellosis (gastrointestinal symptoms, skin alterations) o Swinepox virus (skin alterations)

After the implementation of eradication and control programmes the Member States of the European Union are currently considered to be free of CSF in domestic pigs with few exceptions in South-East Europe. In 2006 was the last CSF outbreak in domestic pigs in Western Europe (Germany). CSF is still endemic in parts of Asia, Africa, Central and South America. North America, Australia and New Zealand have been free of CSF for the last decades.

The disease still occurs in the wild boar populations of several European countries and in recent years outbreaks were recorded, e.g. in Germany, France, Hungary, Romania, Bulgaria, and the Slovak Republic.

In case of an outbreak the following EU regulations directly related to CSF need to be considered: o Council Directive 2001/89/EC (Community Measures for the control of classical swine fever) The main issues this directive is dealing with are: o notification (based on Council directive 82/894/EC) o measurements in holdings with suspected/ confirmed presence of CSFV, in contact holdings, slaughterhouses or means of transport o epidemiological enquiries, o establishment of protection and surveillance zones and measurements o cleaning and disinfection o repopulation of pig holdings after an outbreak o measurements and eradication strategies in case of an outbreak in feral pigs o diagnostic procedures and bio-safety requirements o emergency vaccinations o contingency plans o disease control centres and expert groups This directive should be transposed into national legislation of the single member states until Oct. 2002. o Commission Decision 2002/106/EC This decision approves a Diagnostic Manual establishing diagnostic procedures, sampling methods and criteria for evaluation of the laboratory tests for the confirmation of classical swine fever. This directive has been implemented in national laws of the Member States.

In case of CSF outbreaks in the EU, all pigs in the infected farms have to be slaughtered and the cadavers have to be destroyed. A protection zone (al least 3 km radius) and surveillance zone (at least 10 km radius) have to be established around each outbreak, with restrictions on pig movements (stand-still). An epidemiological investigation with the tracing of the source of infection and the possible spread will be carried out. If appropriate, emergency vaccination may also be used. However, it should be noted that there are restrictions in place for vaccinated animals and their products. Additional ad hoc protection measures may be adopted by the Commission.22

The owner, the person in charge or a veterinary surgeon attending pigs has to report the suspicion to the veterinary authorities immediately. They should not move any pig, carcasses or anything else (e.g feed or waste) suspected of being infected with CSF until an official veterinarian has visited and decided whether it is necessary to conduct further investigations, impose restrictions, or whether CSF can be ruled out.

The European Union prescribes in the Commission Decision 2002/106/EC (approving a Diagnostic Manual) with regard to the Council Directive 2001/89/EC (Community Measures for the control of classical swine fever) that the confirmation of classical swine fever shall be ensured to be based on: a) the detection of clinical signs and post-mortem lesions of disease; b) the detection of virus, antigen or genome in samples of pig tissues, organs, blood or excretions; c) the demonstration of a specific antibody response in blood samples in accordance with the procedures, sampling methods and criteria for evaluation of the results of laboratory tests laid down in the Diagnostic Manual. The definitions in the individual regulations of single EU member states shall at least follow these criteria but can also be more precise or more stringent.

• The World Organisation for Animal Health (OIE), is an intergovernmental organisation responsible for improving animal health worldwide.  
  
• A list of OIE approved experts and laboratories
  
• Classical Swine Fever pages on Defra is the UK’s Department of farming and rural affairs and among other things, deals with outbreaks, surveillance and control of animal diseases.